1. Field of the Invention
The present invention relates to a method of forming a carbon nanotube emitter, and more particularly, to a method of forming a carbon nanotube emitter that has an improved electric field emission.
2. Description of the Related Art
Recently, Carbon Nanotubes (CNTs) have been widely used as a field emitter for a Field Emission Display (FED) devices or for a backlight for Liquid Crystal Display (LCD) devices. Carbon nanotubes have good electron emission characteristics and notable chemical and mechanical durability. Therefore, considerable research is being conducted with regard to the physical properties and applicability of carbon nanotubes.
In an FED device, electrons are emitted from field emitters formed on cathodes due to an electric field between the cathodes and anodes. Emitted electrons collide with the anodes, thereby causing light to be emitted from fluorescent material formed on the anodes.
A micro-tip formed of a metal, such as Molybdenum (Mo), is widely used as the field emitter of the FED device. However, the lifetime of the tip can be shortened because of an atmospheric gas and a non-uniform electric field in the FED devices. Also, there is a limitation as to how much a work function can be lowered to reduce the driving voltage of an FED device using a metal emitter. To solve these problems, a field emitter is formed using carbon nanotubes having a very high aspect ratio, high durability, and excellent electron conductivity.
An important aspect when forming the carbon nanotube emitter is that the carbon nanotube must vertically protrude from a surface of the carbon nanotube emitter. This is because an emission current from the carbon nanotube can differ according to the arrangement state even if the composition of the carbon nanotube is the same. Therefore, it is desirable to configure the carbon nanotube in a vertical arrangement as much as possible.
A carbon nanotube emitter can be formed using a Chemical Vapor Deposition (CVD) method in which the carbon nanotube is directly grown on a substrate, and can also be formed by a paste method in which the carbon nanotube is formed as a paste containing resins. However, the CVD method, despite the ease of arranging the carbon nanotube in a vertical position, can not be readily applied to a glass substrate since it requires heat treatment at a reaction temperature of over 500° C. This method also requires expensive equipment for forming a large area substrate. Furthermore, the density of the carbon nanotube must be properly controlled. Otherwise, the emission current is reduced if the density of the carbon nanotube is too high. On the other hand, the carbon nanotube paste method includes printing the carbon nanotube paste on a substrate, and baking the printed substrate. However, if a surface of the carbon nanotube emitter is not processed, the arrangement of the carbon nanotubes becomes non-uniform, resulting in a non-uniform light emission from the carbon nanotube emitter.